1. Field of the Invention
This invention relates to wood stains and their use on bare wood. More particularly, it relates to water borne wood stains having an elevated viscosity for deterring settlement of the pigment in the stain prior to use of the composition.
2. Brief Description of the Prior Art
Stains that can be used to enhance the grain structure or change the color of the wood or both have been used for years. They generally consist of a pigment, a binder such as an alkyd resin containing a drier, and organic solvents such as mineral spirits, VMP naphtha, kerosene, xylene, toluene or a mixture of these. The pigment in such stains tends to settle and the entire mixture needs prolonged stirring prior to use to obtain a uniform suspension of the pigment in the solvent phase.
To avoid pigment settling, in the last two decades modified alkyds, commonly called gelled alkyds, that give a very high viscosity have been used. An example of such an alkyd is Arothix C301-M-60 produced and sold by Spencer Kellogg Division of Textron, Inc.
Because of environmental considerations related to the flammability and toxicity of the organic solvents, attempts have been made to replace the alkyd or modified alkyd binders with water borne binders such as acrylic emulsions and water dilutable alkyds.
The organic solvent borne alkyds, gelled alkyds, water borne alkyds and acrylic emulsions are relatively expensive. Because they have to be used at fairly high concentrations of 5 to 20 pounds per gallon of stain to reduce pigment settling, they represent an undesirably high cost factor in the stain.
As the need and popularity, due to ease of use, of the water borne coatings has increased, a number of special additives have been developed for use in water borne coatings. These additives include special driers that are stable in aqueous solutions, surface active agents and bubble breakers. Additionally, a variety of water soluble thickeners have been developed. Many of these thickeners when used in small concentrations of 0.1-3 weight percent give high viscosities up to a gelled structure when dissolved in water. These thickeners are not film formers by themselves and have therefore not been considered as replacement for the conventional film forming binders, such as alkyds, modified alkyds, water borne alkyds and polyvinyl or acrylic emulsions.
In recent years several water borne stains have appeared on the market. These are based upon the use of acrylic or polyvinyl acetate emulsions. These emulsions are primarily designed to act as binders, have inherently low viscosities (1-8 poises) and wipe on stains based upon them show substantial pigment settling. To avoid pigment settling, small amounts of synthetic or natural thickeners are often incorporated. The amount of thickener used is generally kept at a very low level as it detracts from the performance characteristics of dried films. Because they do not form films, thickeners by themselves are not used for formulating clear or pigmented coatings. Thus wiping stains, the type of composition to which the present invention is directed, have traditionally been formulated as an extension of the coating formulations.